1. Field of the Invention
The present invention relates to a combination type thin film magnetic head having an inductive type thin film magnetic head element serving as a writing magnetic converting element and a magnetoresistive type thin film magnetic head element serving as a reading magnetic converting element stacked one on the other, and a method of manufacturing the same. More particularly, the present invention relates to an inductive type writing thin film magnetic head having a narrow record track for attaining a high surface recording density on a magnetic record medium by utilizing magnetic materials having a high saturation magnetic flux density, and a method of manufacturing the same.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly. A recent magnetoresistive type thin film magnetic head using a GMR (Giant Magneto-Resistive) element has a surface recording density up to 100 gigabits/inch2. A combination type thin film magnetic head is constructed by stacking an inductive type thin film magnetic head intended for writing information on a magnetic record medium and a magnetoresistive type thin film magnetic head intended for reading information out of the magnetic record medium on a substrate. As a reading magnetoresistive element, a GMR element having a magnetoresistive change larger than a normal anisotropic MR element by 5–15 times has been used. In order to improve a performance of the GMR element, there have been various proposals.
In a normal anisotropic MR element, a single film of a magnetic material showing the magnetoresistive effect is utilized. Many GMR elements have a multi-layer structure having a stack of a plurality of films. There are several mechanisms for generating a resistance change in the GMR element, and the multi-layer structure is dependent upon a mechanism. For instance, a super-lattice GMR film and a glanular film have a simple structure and a large resistance change under a weak magnetic field. A spin-valve GMR film will be suitable for a large scale manufacture.
As stated above, a desired high surface recording density can be simply attained by changing the AMR element by the GMR element as long as the reproducing thin film magnetic head is concerned, and a surface recording density could be further increased by utilizing a magnetic material having a higher magnetoresistive sensitivity. A performance of a reproducing head element is also dependent upon a pattern width in addition to the above mentioned selection of material. The pattern width includes a MR height and track width. A track width is determined by a photolithography process and a MR height is determined by an amount of polishing for forming an air bearing surface (ABS).
At the same time, the performance of the recording magnetic head is also required to be improved in accordance with the improvement of the performance of the reproducing magnetic head. In order to increase a surface recording density, it is necessary to realize a high track density on a magnetic record medium. To this end, a pole portion of the recording thin film magnetic head element has to be narrowed in a sub-micron order by utilizing the semiconductor manufacturing process. However, upon decreasing a track width by utilizing the semiconductor manufacturing process, there is a problem that a sufficiently large magnetic flux could not be obtained due to a miniaturized structure of the pole portion. In order to solve such a problem, there has been proposed to make at least a pole portion of a recording head element of a magnetic material having a high saturation flux density (Hi-Bs material).
FIGS. 1–5 show successive steps of a method of manufacturing a conventional combination type thin film magnetic head. In these drawings, A represents a cross sectional view cut along a plane perpendicular to the air bearing surface ABS and B denotes a cross sectional view of a pole portion cut along a plane parallel to the air bearing surface ABS. FIG. 6 is a plan view showing schematically the structure of the known combination type thin film magnetic head.
As shown in FIG. 1, an alumina (Al2O3) insulating film 12 having a thickness of about 2–3 μm is deposited on a substance 11 made of AlTiC. Next, a bottom shield film 13 made of a magnetic material for magnetically shielding a GMR reading head element from an external magnetic field. On the bottom shield film 13, a shield gap film 14 made of alumina is formed with a thickness of 300–350 Å by sputtering. Then, a GMR film 15 having a given layer-structure is formed, and lead electrodes 16 for the GMR film are formed by a lift-off process. Next, a top shield gap film 17 made of alumina is formed with a thickness of 300–350 Å by sputtering, and a magnetic film 18 serving as a top shield film is formed with a thickness of about 3 μm.
Next, an isolation film 19 made of alumina is formed with a thickness of about 0.3 μm for isolating the reading GMR head element from a writing induction type thin film magnetic head element to suppress noise in a reproduced output from the GMR head element. After that, a bottom pole 20 of the recording head element made of permalloy is formed with a thickness of 1.5–2.0 μm as illustrated in FIG. 1. It should be noted that in the drawings a ratio of thickness of various portions does not exactly correspond to an actual ratio. For instance, the isolation film 19 is shown to have a smaller thickness.
Next, as depicted in FIG. 2, on the bottom pole 20, is formed a write gap film 21 having a thickness of about 2000 Å, and a top pole 22 made of permalloy which is a magnetic material having a high saturation magnetic flux density is formed in accordance with a given pattern. At the same time, a bridge film 23 for magnetically coupling the bottom pole 20 with the top pole 22 at a back-gap is formed. The top pole 22 and bridge film 23 are formed by plating with a thickness of about 3–4 μm.
Then, in order to avoid a widening of an effective track width, i.e. in order to prevent a magnetic flux from extending at the bottom pole 20 during a writing operation, the write gap film 21 and the underlying bottom pole 20 around the top pole 22 are etched by ion milling to form a so-called trim structure. After that, forming an alumina insulating film 24 having a thickness of about 3 μm over a whole surface, a surface is flattened by the chemical mechanical polishing (CMP) as shown in FIG. 3.
Next, as illustrated in FIG. 4, a thin film coil 25 is formed on the flattened surface by the electrolytic plating of Cu in accordance with a given pattern, and an insulating film 26 which supports the thin film coil 25 in an electrically insolated manner is formed by photoresist. Next, as depicted in FIG. 5, a top pole 28 made of permalloy is formed with a thickness of about 3 μm such that the top pole 22 and bridge film 23 are coupled with each other by the top pole 28. Next, a whole surface is covered with an overcoat film 29 made of alumina. It should be noted that during the formation of the top pole 28, an electrically conductive film 29 for connecting the thin film coil 25 to an external circuit is formed with a same magnetic material as that of the top pole 28. Finally, an end surface into which the GMR film 15, write gap film 21, top pole 22 and so on are exposed is polished to form an air bearing surface ABS to complete a slider.
FIG. 6 shows a cross sectional view and a plan view illustrating the structure of the known combination type thin film magnetic head manufactured in the manner explained above. The bottom pole 20 has a large area, but the top poles 22 and 28 have a smaller area than the bottom pole. One of factors determining the performance of the writing head element is a throat height TH. The throat height TH is a distance from the air bearing surface ABS to an edge of the insulating film 26 which isolates the thin film coil 25 in an electrically insulating manner, and this distance is desired to be short. One of factors determining the performance of the reading head element is an MR height MRH. This MR height (MRH) is a distance from the air bearing surface ABS into which one edge of the GMR film 15 is exposed to the other edge of the GMR film. During the manufacturing process, a desired MR height MRH is obtained by controlling an amount of polishing the air bearing surface ABS.
There is another factor determining the performance of the thin film magnetic head together with the above mentioned throat height TH and MR height MRH. This factor is an apex angle θ, which is defined by an angle formed by a tangential line to a side wall of the insulating film 26 isolating the thin film coil 25 and an upper surface of the top pole 28. In order to miniaturize the thin film magnetic head, it is required to increase the apex angle θ as large as possible.
Now problems in the known combination type thin film magnetic head mentioned above will be explained. After forming the insulating film 26 such that the thin film coil 25 is supported by the insulating film in an electrically insulating manner, the top pole 28 is formed. In this case, the top pole 28 has to be formed into a given pattern along the side wall of the insulating film 26. To this end, a photoresist is formed with a thickness of 3–4 μm at a step of the insulating film 26 having a height of about 7–10 μm. Now it is assumed that at the side wall of the insulating film 26, the photoresist should have a thickness of at least 3 μm, a thickness of the photoresist at the bottom of the step would become thick such as 8–10 μm. Since a width of record track of the writing head is mainly determined by a width of the top pole 22, it is not necessary to miniaturize the top pole 28 compared with the top pole 22, but if the track width of submicron order such as 0.2 μm is desired, the pole portion of the top pole 28 should be miniaturized in the order of submicrons.
Upon forming the top pole 28 into a desired pattern by plating, the photoresist has to be deposited on the top pole 22 and insulating film 26 having the step of more than 10 μm such that the photoresist has a uniform thickness. Then, the photoresist is subjected to the exposure of light to form the top pole 28 having the pole portion of submicron order. That is to say, a pattern of submicron order should be formed with the photoresist having a thickness of 8–10 μm. When the pole portion 28 is formed by plating, a seed layer made of permalloy serving as an electrode is previously formed. During the light exposure of the photolithography, light is reflected by the permalloy seed layer, and a desired pattern might be deformed. Therefore, it is quite difficult to form the pattern of submicron order precisely.
In order to improve the surface recording density, it is required to miniaturize the pole portion as explained above. Then, the miniaturized pole portion must be made of a magnetic material having a high saturation magnetic flux density. IN general, FeN and FeCo have been known as magnetic materials having a high saturation magnetic flux density. However, these magnetic materials could not be easily formed by sputtering into a film having a given pattern. It has been known to shape the sputtered film into a given patter by the ion milling. However, etching rate is too slow and a track width of submicron order could not be controlled precisely.
NiFe, CoNiFe, FeCo have been known to have a high saturation magnetic flux density, and these magnetic materials could be formed into a given pattern by plating. For instance, Fe rich NiFe (more than 50%) has a saturation magnetic flux density of 1.5–1.6 tesla (T), and a composition could be controlled stably. However, in order to realize a surface recording density of 80–100 gigabits/inch2, a track width has to be not larger than 0.2 μm. Then, there would be required to use a magnetic material having a higher saturation magnetic flux density. There has been proposed to form a magnetic film by plating using CoNiFe. However, this magnetic material could provide the magnetic faculty of about 1.8–2.0 T. In order to realize the surface recording density of about 80–100 gigabits/inch2, it is desired to use a magnetic material having a high saturation magnetic flux density such as 2 T.
A high frequency performance of the induction type thin film magnetic head is also determined by a magnetic path length which is defined as a length from the throat height zero position to the back-gap. A high frequency performance of the thin film magnetic head is improved by shortening the above mentioned magnetic path length. It would be possible to shorten the magnetic path length by reducing a pitch of successive coil windings of the thin film coil 11, but this solution has a limitation. Then, there has been proposed to construct the thin film coil to have two coil layers. Upon forming the two-layer thin film coil, after forming a first thin film coil layer, an insulating film of photoresist is formed with a thickness of about 2 μm. This insulating layer has a round outer surface, and thus upon forming a second thin film coil layer, a seed layer for electrolytic plating has to be formed on an inclined portion. Therefore, upon etching the seed layer by the ion milling, a portion of the seed layer hidden by the inclined portion could not be removed sufficiently and coil windings might be short-circuited. Therefore, the second thin film coil has to be formed on a flat surface of the insulating layer.
For instance, it is now assumed that a thickness of the first thin film coil layer is 2–3 μm, a thickness of the insulating film formed on the first thin film coil layer is 2 μm, and an apex angle of the inclined portion of the insulating film is 45–55°, an outer surface of the second thin film coil layer must be separated from the throat height zero reference position by a distance of 6–8 μm which is twice of a distance from the throat height zero reference position to the outer surface of the first thin film coil layer. Then, a magnetic path length would be longer accordingly. When the thin film coil has space/line of 1.5 μm and a total number of coil windings is eleven, six coil windings are provided in the first thin film coil layer and five coil windings are formed in the second thin film coil layer. Then, a length of the whole thin film coil becomes 11.5 μm. In this manner, in the known thin film magnetic head, a magnetic path length could not be shortened, and a high frequency property could not be improved.